Energy absorbing device



Aug. 27, 1940. T. M. GLUYAS. JR 313,103

ENERGY ABSORBING DEVICE Filed larch 15, 1959 Load.

Carrier Frequency Sou-roe Z7 Vraii Patented Aug. 27, 1940 UNITED STATESPATENT OFFICE ENERGY ABSORBING DEVICE of Nevada Application March 15,1939, Serial No. 262,041

8 Claims.

This invention relates to improvements in controllable energydissipating means for use in modulating systems of the energy absorptiontype. More particularly, the invention relates to energy dissipatingmeans employing space discharge devices, and to a method of and meansfor eliminating the undesired effects produced by the fortuitouscapacities in the space discharge devices.

In a copending application of William N. Parker, Serial No. 84,534,filed June 10, 1936, there is disclosed and claimed a modulating systemof the energy absorption type which is particularly useful in thegeneration of a modulated high frequency carrier signal for televisionpurposes where a wide band of frequencies must be transmitted forsatisfactory picture reproduction. In that application, there areprovided means for accomplishing modulation at a high level and with aconsiderably, greater efficiency, as well as for a wider band offrequencies, than is possible with prior systems. The principal featureof the Parker system resides in shunting a high impedance source ofcarrier frequency energy by a controllable energy dissipating impedancewhich is variable in response to a modulating signal. In order that thesystem shall function in the most satisfactory manner, it is desirablethat the modulating impedance be purely resistive, variable in magnitudein response to a modulating signal, and reduceable to zero for areasonable value of the modulating signal on the valleys of modulation.The Parker application discloses a very satisfactory form of modulatingimpedance comprising a plurality of space discharge devices which serveto dissipate carrier frequency energy and thereby generate sidebandcomponents in response to the modulating signal which is impressed ontheir grids. The resulting impedance, which is a combination of theplate impe iances of the space discharge devices, is inverter! by meansof a quarter wave-length transrmssion line or other suitableimpedance-inverting means. Thus there is produced an impedance which isvariable from zero to a very high value, as clearly set forth in thesaid Parker application.

It is observed in the Parker application that a certain amount ofcapacitive reactance is introduced at the modulator endof theimpedanceinverter due to the inherent capacitance between the severalanodes, grids and cathodes of the energy dissipating tubes. Thiscapacitive component is inverted by the transmission line andcontributes an inductive component to the impedance appearing at theother end of the line.

ASeveral means are disclosed in the Said Parker application and in asubsequent continuation-inpart thereof, Serial No. 252,204, filedJanuary 21, 1939 whereby it is possible to overcome the effect of thetube capacitance and to produce a modulating impedance which issubstantially purely resistive. One method consists in shunting theoutput circuits of the energy dissipating tubes by an inductance ofsuitable magnitude to tune out the capacitance of the tubes at, thecarrier frequency. Another method consists in shortening the effectiveelectrical length of the transmission line or other impedance-invertingmeans coupled to the modulating tubes. In this case a capacitance may beintroduced at the load end of the impedance inverter. This capacitance,in conjunction with that of the tubes at the other end of the line,operates to fill out the shortened line and to make its electricallength equal to one quarter wave length of the carrier frequency.

The present invention is directed particularly to this phase of theproduction of an energy dissipating device of the type disclosed in thesaid Parker applications. Its principal object is to provide an improvedmeans for obtaining an inductive component in shunt with the outputs ofthe energy absorbing tubes in such a device. An advantage of the methodof this invention is that it permits this inductive component to beintroduced without the use of an actual physical inductance shuntedacross the outputs of the said modulating tubes.

Further features of the invention will appear from the followingdescription and the accompanying drawing in which:

Fig. 1 is a schematic diagram of one embodiment of the invention;

Fig. 2 is an explanatory diagram which will be referred to in explainingthe operation of the system of Fig. 1; and

Fig. 3 is a schematic diagram showing a modification of a portion of thecircuit of Fig. 1.

Referring first to Fig. 1, there is shown a modulating system which,aside from the features of the present invention is substantially thesame as that shown in the aforementioned continuationin-part applicationSerial No. 252,204. For convenience of showing and for purposes ofemphasis, only that portion of the circuit which constitutes themodulating impedance is shown in detail, the other portions being givenconventionalized representations. Carrier frequency energy is obtainedfrom the source S which is coupled to a junction point 2 by means of atransmission line I having an electrical length substantially equal toone-quarter wave length of the signal.

' gether.

According to the Parker system, the impedance of the carrier source islow and is inverted to appear as a high impedance at the junction point2. Thus there is produced at the junction point 2 an effective highimpedance carrier frequency source. A second quarter wave line 3connects the junction point with the load L which may be an antennasuitable for radiating the carrier frequency signal. Modulating tubes 4have their plates coupled to the junction point 2 through the line 5.The electrical length of this line is not necessarily equal toone-quarter wave length but the line may be of such a length as to form,in

conjunction with the capacities appearing at its two ends, an impedanceinverter of effective electrical length equal to one-quarter wavelength. between the plates of the tubes and the junction point. Suchimpedance-inverter is resonant at a frequency within a certain frequencyrange comprising frequencies in the vicinity of the carrier frequency,and it forms an impedance substantially inversely proportional to theeffective impedance of the tubes 4 for wave signals within said range.Modulating voltage is supplied between the grids and cathodes of thetubes 4 through the chokes l3 from the source Em, the grids and cathodesrespectively being tied to- A return lead 6 is provided between thecathodes of the modulating tubes and a center tap on the inductance 1shunted across the junction point 2, as taught by Parker, to provide apath for rectification products resulting from the modulation process.The inherent capacity introduced by the modulator tubes is representedat 8, and any capacity which may appear at the junction point due to theend effects of the transmission lines, as a result of the junction ofseveral lines at a single point, or which may purposely be introduced atthat point, is represented at 9.

According to the present invention, an inductive reactance is, ineffect, made to appear in the output circuits of the space dischargedevices 4 by causing a component of the carrier frequency plate current,when considered as flowing out of the line 5, to lag the carrierfrequency plate voltage by ninety degrees. This is accomplished byapplying to the grids of the modulator tubes a voltage of carrierfrequency which lags the voltage in the plate circuit by the sameamount. Such a voltage is obtained by changing the phase of the voltagederived from any one of a number of points in the circuit at whichcarrier frequency voltage appears. The change in phase may be producedby a transmission line of appropriate electrical length. For example, inFig. 1 the carrier voltage is derived from the junction point 2 and isfed back in the opposite phase to the grids of the tubes 4 by means ofthe transmission line H] whose electrical length is substantially equalto a half-wave length or an odd number of halfwave lengths. It will benoted that blocking condensers are interposed between the transmissionline ill and the grids of tubes 4 to prevent shortcircuiting of themodulating source Em while permitting the desired feed back of thecarrier voltage. The voltage on the plates of the tubes lags that at thejunction point by ninety degrees, and hence a component of the platecurrent will lag the plate voltage by ninety degrees. The manner inwhich this obtains will be seen more clearly upon reference to Fig. 2which is a vector diagram showing the inter-relations in phase betweenthe various currents and voltages. The magnitude of the carrierfrequency voltage in the grid circuit and that of the lagging componentof plate current are exaggerated for purposes of clarity. In the diagramthe following vector symbols are used:

The magnitude of the voltage which must be fed back will depend on themagnitude of the capacitance for which it is desired to compensate. Forexample, when the capacity shunted across the junction end of the lineis negligible it may be desirable to neutralize. or balance out theentire tube capacity in "which case the electrical length of the line 5itself may be made equal to a quarter wave length. On the other hand,when an appreciable capacity appears at the junction point, it ispreferable to have a certain amount of the tube capacity unbalanced toform in conjunction with the line 5 and the junction capacity animpedance inverter whose effective electrical length is a quarter wavelength of the carrier frequency. In this case the line itself may beappropriately shortened. Whatever the magnitude of the capacitivecomponent desired t may be obtained by-applying to the grids of thetubes 4 a carrier frequency voltage of suitable magnitude determined,for example, by the choice of the characteristic impedance of thetransmission line I.

Fig. 3 illustrates another method of feeding back carrier frequencyvoltage. Only that portion of the circuit is shown which is associatedimmediately with the modulator tubes 4. The remainder of the system maybe similar to Fig. l. The principal modification introduced in Fig. 3 isthe derivation of carrier frequency voltage from the plates of themodulating tubes. In the embodiment shown this is accomplished by meansof high resistances H and capacitances l2, the resistors being connectedbetween the plates and grids, and the condensers being connected betweenthe grids and cathodes of the respective tubes. With the resistancessufficiently large by comparison with the carrier frequency reactance ofthe condensers l2, the current through the series combination will be inphase with the plate voltage. The carrier voltage impressed on the gridswill lag this current and the plate voltage by approximately inaccordance with the diagram of Fig. 2.

The foregoing description of the invention has dealt solely with itsapplication in a particular type of modulating system with reference totwo embodiments thereof but this should not be regarded as restrictingthe method to application only in the arrangements shown. For example,both of the embodiments show a pair of tubes operating in push-pull togive greater efficiency and to obviate the need for a D. C. supply totheir plates. It will appear that it would be feasible under certaincircumstances to employ but a single tube or a plurality of tubes towhich the method herein disclosed could be applied with but a slightmodification of the apparatus here disclosed. My invention contemplatessuch varia tions and may be regarded as applicable to modulating systemsin general subject only to the restrictions imposed by the followingclaims.

I claim:

1. In a device for dissipating electrical wave energy having a frequencywithin a certain range, at a rate variably in response to a controlsignal; energy dissipating means including a space discharge devicehaving an anode, a cathode, and a control grid, said space dischargedevice having a fortuitous capacity appearing between its anode and itscathode; a source of a control signal coupledto the grid circuit of saidspace discharge device for controlling the energy dissipation therein;an impedance-inverter comprising a transmission line resonant at afrequency within said range, said line having one end coupled to theanode circuit of said space discharge device for forming an impedancesubstantially inversely proportional to the impedance of saiddissipative means for wave signals within said range; and furthertransmission line means having an input circuit and an output circuitand having an electrical length substantially equal to an odd number ofhalf wavelengths for wave signals within said range, said last-mentionedmeans having its input circuit coupled to the other end of said firsttransmission line and its output circuit coupled to the grid circuit ofsaid space discharge device, for supplying thereto a signal whosefrequency is the same as that of the energy to be dissipated and whosephase is substantially in laggingrelation with respect to the signal inthe anode circuit of said space discharge device.

2. In a system for dissipating electrical wave energy, at a ratevariable in response to a control signal; a source of wave energy to bedissipated; an energy dissipating space discharge device having at leasta cathode, a grid, and an anode; means for coupling said anode to saidsource and for forming an effective impedance invefler for inverting theimpedance of said space discharge device; a source of control signalcoupled to the grid of said space discharge device for controlling thedissipation of energy thereby; means for deriving from the system asignal of predetermined magnitude whose frequency is substantially equalto that of said wave energy and whose phase is substantially in 90lagging relation with respect to the signal appearing at said anode; andmeans for applying said derived signal to the grid of said spacedischarge device, whereby an inductive component is introduced in theimpedance appearing between said anode and said cathode, said inductivecomponent varying in such a manner with the control signal applied tosaid grid that said inverted impedance is substantially purely resistivefor all values of control signal applied to said grid.

3. In a system for dissipating electrical wave energy having a frequencywithin a certain range, at a rate variable in response to a controlsignal; energy dissipating means including a space discharge devicehaving an anode, a cathode and a control grid, said space dischargedevice having fortuitous capacity appearing between its anode and itscathode; a source of a control signal coupled to the grid circuit ofsaid space discharge device for controlling the energy dissipationtherein; means coupled to the anode circuit of said space dischargedevice forming an effective impedance inverter resonant at a frequencywithin said range to invert the impedance of said dissipative means forwave signals within said range; means for deriving from the system asignal whose frequency is the same as that of the energy to bedissipated and whose phase is substantially in 90 lagging relation withrespect to the signal in the anode circuit of said space dischargedevice; and means for applying said derived signal to the grid circuitof said space discharge device, the magnitude of said derived signalbeing such as to substantially neutralize the undesired capacity of saidspace discharge device, whereby the inverted impedance of said spacedischarge device is caused to be substantially purelyresistive.

4. In a system for dissipating electrical wave energy having a frequencywithin a certain range, at a rate variable in response to a controlsignal; energy dissipating means including a space discharge devicehaving an anode, a cathode and a control grid, said space dischargedevice having fortuitous capacity appearing between its anode and itscathode; a source of a control signal coupled to the grid circuit ofsaid space discharge device for controlling the energy dissipationtherein; a transmission line coupled to the anode circuit of said spacedischarge device, said transmission line being of proper length to formin cooperation with said fortuitous tube capacity an eifective impedanceinverter resonant at a frequency within said range to invert theimpedance of said dissipative means for wave signals within said range;means for deriving from the system a signal whose frequency is the sameas that of the energy to be dissipated and whose phase is substantiallyin 90 lagging relation with respect to the signal in the anode circuitof said space discharge device; and means for applying said derivedsignal to the grid circuit of said space discharge device, whereby aninductive component is introduced in the impedance appearing betweensaid anode and said cathode, said inductive component varying in such amanner with the control signal applied to said grid that said invertedimpedance is substantially purely resistive for all values of controlsignal applied to said grid.

5. In a system for dissipating electrical wave energy having a frequencywithin a certain range, at a rate variable in response to a controlsignal; a source of wave signal energy to be dissipated, said sourcehaving a capacitive reactive impedance component appearing'across itsoutput terminals; energy dissipating means including a space'dischargedevice having an anode, a cathode and a control grid, said spacedischarge device having a fortutious capacity appearing between itsanode and its cathode; a source of a. control signal coupled to the gridcircuit of said space discharge device for controlling the energydissipation therein; a transmission line connected between the anodecircuit of said space discharge device and said first source, saidtransmission line being of proper length toform in cooperation with saidfortuitous tube capacity and the capacitive reactance of said firstsource an effective impedance inverter resonant at a frequency withinsaid range for inverting the impedance of said dissipative means forwave signals within said range; means for deriving from the system asignal whose frequency is thesame as that of the energy to be dissipatedand whose phase is substantially in 90 lagging relation with respect tothe signal in the anode circuit of said space discharge device; andmeans for applying said derived signal to the grid circuit of said spacedischarge device, whereby an inductive component is introduced in theimpedance appearing between said anode and said cathode, said inductivecomponent varying in such a manner with the control signal applied tosaid grid that said inverted impedance is substantially purely resistivefor all values of control signal applied to said grid.

6. In a device for dissipating electrical wave energy having a frequencywithin a certain range, at a rate variable in response to a controlsignal; energy dissipating means including a space discharge devicehaving an anode, a cathode and a control grid, said space dischargedevice having a fortuitous capacity appearing between its anode and itscathode; a source of a control signal coupled to the grid circuit ofsaid space discharge device for controlling the energy dissipationtherein; means coupled to the anode circuit of said space dischargedevice for forming an effective impedance inverter resonant at afrequency within said range to invert the impedance of said dissipativemeans for wave signals within said range; and transmission line meanshaving an input circuit and an output circuit and having an electricallength substantially equal to an odd number of half-wave lengths forwave signals within said range, said last-mentioned means having itsinput circuit coupled to said impedance inverter and its output circuitcoupled to the grid circuit of said space discharge device, forsupplying thereto a signal whose frequency is the same as that of theenergy to be dissipated and whose phase is substantially in 90 laggingrelation with respect to the signal in the anode circuit of said spacedischarge device, whereby an inductive component is introduced in theimpedance appearing between said anode and said cathode, said inductivecomponent varying insuch a manner with the control signal applied tosaid grid that said inverted impedance is substantially purely resistivefor all values of control signal applied to said grid.

'7. In a device for dissipaating electrical wave energy having afrequency within a certain range, at a rate variable in response to acontrol signal; energy dissipating means including a space dischargedevice having an anode, a cathode, and a control grid, said spacedischarge device having a fortuitous capacity appearing between theanode and its cathode; a source of a control signal 'coupled to the gridcircuit of said space discharge device for controlling the energydissipation therein; means coupled to the anode circuit of said spacedischarge device for forming an effective impedance inverter resonant ata frequency within said range to invert the impedance of saiddissipative means for wave signals within said range; means for derivinga signal from the anode circuit of said space discharge device of thesame frequency as the energy to be dissipated; means for shifting thephase of said derived signal so as to cause it to lag the voltage in theanode circuit of said space discharge device by approximately 90; andmeans for applying said derived signal to the grid circuit of said spacedischarge device, whereby an inductive component is introduced in theimpedance appearing between said anode and said cathode, said inductivecomponent varying in such a manner with the control signal applied tosaid grid that said inverted impedance is substantially purely resistivefor all values of control signal applied to said grid.

8. In a device for dissipating electrical wave energy having a frequencywithin a certain range, at a rate variable in response to a controlsignal;

energy dissipating means including a space discharge device having ananode, a cathode and a control grid, said space discharge device havinga fortuitous capacity appearing between its anode and its cathode; asource of a control signal coupled to the grid circuit of said spacedischarge device for controlling the energy dissipation therein; meanscoupled to the anode circuit of said space discharge device for formingan effective impedance inverter resonant at a frequency within saidrange to invert the impedance of said dissipative means for wave signalswithin said range; and means including a transmission line for supplyingto the grid circuit of said space discharge device a signal whosefrequency is the same as that of the energy to be dissipated and whosephase is substantially in 90 lagging relation with respect to the signalin the anode circuit of said space discharge device, whereby aninductive component is introduced in the impedance appearing betweensaid anode and said cathode, said inductive component varying in such amanner with the control signal applied to said grid that said invertedimpedance is substantially purely resistive for all values of controlsignal applied to said grid.

THOMAS M. GLUYAS, JR.

